1. Field of the Invention
This invention relates to a variable pressure reducing device to reduce the pressure and control the flow of high pressure liquids. In particular, the invention relates to a rod-in-tube-type pressure reducing device with an improvement in construction of the rods to smooth the flow of liquid through the device and an improvement in the sealing means to provide easier adjustability of the device.
2. Background of the Art
Numerous applications of high pressure fluid systems require, at some point in the system, reduction of the pressure to allow safe handling of the fluid. For instance, a sample withdrawn from a steam and hot water system in a power plant must be reduced in pressure before the sample can be introduced into analyzing instrumentation or handled safely by plant personnel. A number of devices are used in the power plant industry to reduce the high pressure of steam and hot water, such as fixed orifice valves or pressure regulators, but material erosion frequently experienced in such devices can lead to loss of function. Capillary tubing, also commonly used to reduce high pressure in liquid samples, may become blocked by crud or scale, requiring complete shutdown of the sample line while the capillary tubing is cleaned or replaced.
Another type of device for reducing high pressure in liquids is applicant's earlier version of a variable pressure reducing element (VREL.TM.). The VREL is a rod-in-tube device in which the pressure of an incoming liquid is reduced as the liquid is forced to travel through a narrow gap between a stepped rod and the inner diameter of a tube. Because the work is done over the entire length of the stepped rod, localized stresses are held to a minimum, resulting in a very long service life compared with orifice valves and pressure regulators in which the pressure drop is taken over a very short distance. The flow through the VREL, or the pressure drop across it, can be adjusted while the liquid is flowing through the device by changing the position of the rods in the tubes. Turning the handle in one direction or the other moves the rods in or out of the tubes. If crud blocks the flow of liquid, the rods can be fully retracted to allow the high pressure liquid to blow the dirt through the device.
This earlier version of the VREL, however, has a number of drawbacks and disadvantages. The flow past the steps in the stepped rod causes turbulence and unsteady liquid flow, which is undesirable particularly when the device is used in connection with applicant's new automated sample conditioning panel (which is the subject of a co-pending application). Scale and crud also have a tendency to build up on the steps of the stepped rod, inhibiting flow through the device.
In the earlier version of applicant's VREL device, a packing seal, comprised of a thick Teflon .TM. ring sandwiched between two washers and compressed ("packed") within a valve gland by a threaded nut, caused high compressive forces making it difficult to adjust the device. A leak in the seal would typically be fixed by plant personnel merely tightening the nut further, which in turn simply increased the compressive forces and making it further difficult to adjust the device.